Microstrip antennas with a lightweight, low profile, low cost and planar structure have been replacing bulky antennas. The length of a rectangular microstrip antenna is about a half wavelength within the dielectric medium under a radiating patch. A half wavelength is still relatively large at UHF and VHF frequencies and these frequencies also impose size limitations that can result in bulky and cumbersome antenna structures. However, microstrip antennas, particularly the electrically small microstrip antennas, have a rather narrow bandwidth. This narrow bandwidth has been tolerated because most modern communications systems generally only need a few distinct frequencies, e.g. one to transmit and one to receive, rather than a continuous spectrum of operating frequency. The disadvantages, drawbacks, limitations and shortcomings of conventionally-sized narrow-band microstrip antennas have created a long-felt need for more compact multiple band antenna structures at lower frequencies that are also low-cost, rugged and conformal in nature. Up until now, it has not been possible to employ planar microstrip antennas without the disadvantages, limitations and shortcomings associated with antenna length and size.
Aside from the need for compact multiple band antenna structures, the prior art narrowband microstrip antennas have suffered from a number of other problems. One continuing problem with prior art narrowband microstrip antennas is unwanted antenna length of a half wavelength length within the dielectric medium, and they also suffer from other size-related drawbacks and disadvantages such as excessive cost and cumbersomeness. Thus there has been a long-felt and unsatisfied need for a multiple band electrically small microstrip antenna for the VHF and UHF frequencies.
The present invention makes it possible to fulfill the need for a significantly reduced antenna length and an electrically small multi-band antenna without suffering from the disadvantages, shortcomings and limitations of lengthy, costly and cumbersome conventional microstrip antennas.